1. Field of the Invention
The present invention relates to a photoelectric converter device, and more particularly to improvements in such device using and equipped with one-dimensional line sensors in, for example, image sensor means of the close contact type of a facsimile.
2. Description of the Prior Art
There have been recently developed (a) a photoelectric converter system in which the photoelectric converter element array has a size equal to that of one side of the original, so that there is formed an optical image at the ratio of 1:1 with respect to the respective photoelectric converter elements through the optical fiber array and the lens array, and (b) a photoelectric converter system in which, with the photoelectric converter element array closely contacted with the surface of the original, the original is illuminated through light guide windows in the photoelectric converter element substrate and the reflected light from the original are read by the photoelectric converter elements.
These systems normally use reading circuits of a photoelectric converter system of the electric charge storage type, in which electric signals are supplied through electric charge storage means, as shown in FIGS. 1 and 2.
FIG. 1 illustrates a basic unit for a photoelectric converter system of the electric charge storage type in which a photoelectric converter element 1 has electric charge storage means. When a switch 3 is opened, a bias voltage is applied to a storage capacitor 1b connected in parallel to a photodiode 1a, by a bias power supply 2. A predetermined amount of electric charge is therefore stored in the capacitor 1b. The photodiode 1a receives the reflected light from the original, and electric charge stored in the storage capacitor 1b is discharged correspondingly to the amount of photoelectric conversion made by such light reception. Thereafter, when the analogue switch 3 is suitably closed, a voltage generated at load resistance 4 is sent to an output terminal 5. A slight signal is thus detected. A coupling capacitor 6 is disposed, and the analogue switch 3 has a capacitance 7.
FIG. 2 illustrates the circuit of a photoelectric converter element array in which arranged are in a one-dimensional manner a plurality of the basic units, one of which is shown in FIG. 1.
Driving a shift register 8 causes the analogue switches 3 successively to be opened and closed in time sequence. Electric signals thus sent from the photoelectric converter elements 1 pass through an electrically common output line 10 via the analogue switches 3 respectively corresponding to the photoelectric converter elements 1, and a voltage generated at the load resistance 4 is sent to the output terminal 5.
According to the prior art above-mentioned, it is unavoidable that the control logic signal lines 9 are located adjacent the output line 10. Such arrangement causes noise from the control logic signal lines 9 to be introduced into the output line 10, thereby increasing noise in output signals.
In order to overcome such problem, it is proposed to provide the output line 10 with an electrostatic shield. It is however found from tests conducted by the inventor with such shield used that capacitance was increased between the output line 10 and grounding lines, thereby provoking a decrease in the output voltage.
According to the prior art in FIG. 1, a switching noise generated at the analogue switch 3 flows to the grounding line through the load resistance 4. Such noise is therefore superposed onto an output signal, thereby decreasing the S/N ratio.